Barrier layers are commonly used between conductive layers in all kinds of semiconductor devices. Barrier layers can prevent spiking between conductive layers, prevent electromigration failures and generally improve the contact between one conductor and another. Barrier layers are particularly useful and critical in high speed, highly integrated semiconductor devices that use copper as the interconnect material. The conductive interconnect materials of a semiconductor device contact each other through openings formed in insulative dielectric materials that otherwise insulate the various conductive interconnect layers from one another in non-contact regions. The majority of any conductive interconnect feature is therefore bounded by a dielectric, i.e., it forms an interface with the dielectric. When a barrier layer is used in conjunction with a conductive interconnect, it is formed either above or below (or both) the conductive interconnect layer and therefore forms an interface with the insulating dielectric in many areas, as well as an interface with another conductor in the critical contact area. A single barrier layer is therefore disposed between conductors in one area and between one of the conductors and a dielectric, in another area. For example, in single damascene or dual damascene technology, the barrier layer may be formed below the conductor that fills the damascene opening. The barrier layer therefore lines the sides of the opening, interfacing with a dielectric, and is also disposed between two conductors at the bottom of the opening where contact is made to a subjacent conductive material.
Conventional barrier layers typically have strengths and shortcomings. For example, some barrier layers adhere well to conductive materials but do not adhere well to dielectric materials. Conversely, other barrier materials adhere well to dielectric materials but do not adhere well to conductive materials. Some barrier materials provide good barrier qualities with respect to some metals, but not others. In general, barrier layers may include superior or poor qualities with respect to electromigration suppression, contact resistance, wettability, step coverage, resistivity, and so on, depending on where they are used. The reason that a conventional barrier layer typically includes shortcomings in addition to desirable qualities is because conventional barrier layers are typically formed of one barrier material that may provide desirable barrier qualities with respect to some materials but not others. No one barrier material is perfect. For example, if the one barrier material provides superior adhesion to conductive layers, it may conversely provide poor adhesion qualities with respect to dielectric layers. While such an exemplary barrier layer may be a superior barrier material between conductive features, it would likely be deficient when disposed between the conductive material and a dielectric.
It would therefore be desirable to provide a barrier layer, such as a composite barrier layer, having superior qualities for its chosen application. For example, it would be desirable to provide a barrier layer that provides superior barrier qualities and adheres well to all materials it interfaces with throughout the semiconductor device. This invention is directed to such a composite barrier layer.